Cancer is the commonest cause for death among all of the causes for death, and therapies carried out therefor at present are mainly surgical treatment in combination with radiotherapy and chemotherapy. In spite of the developments of new surgical methods and discovery of new anti-cancer agents in recent years, treatment results of cancers are not improved very much at present except for some cancers. In recent years, by virtue of the development in molecular biology and cancer immunology, cancer antigens recognized by cytotoxic T cells reactive with cancers, as well as the genes encoding the cancer antigens, were identified, and expectations for antigen-specific immunotherapies have been raised (Non-patent Literature 1).
In immunotherapy, to reduce side effects, it is necessary that the peptide, polypeptide or protein recognized as the antigen exist hardly in normal cells and exist specifically in cancer cells. In 1991, Boon et al. of Ludwig Institute in Belgium isolated a human melanoma antigen MAGE 1, which is recognized by CD8-positive T cells, by a cDNA-expression cloning method using an autologous cancer cell line and cancer-reactive T cells (Non-patent Literature 2). Thereafter, the SEREX (serological identifications of antigens by recombinant expression cloning) method, wherein tumor antigens recognized by antibodies produced in the living body of a cancer patient in response to the cancer of the patient himself are identified by application of a gene expression cloning method, was reported (Non-patent Literature 3; Patent Literature 1), and several cancer antigens have been isolated by this method (Non-patent Literatures 4 to 9). Using a part thereof as targets, clinical tests for cancer immunotherapy have started.
On the other hand, as in human, a number of tumors such as mammary gland cancer, leukemia and lymphoma are known in dogs and cats, and they rank high also in the statistics of diseases in dogs and cats. However, at present, no therapeutic agent and prophylactic agent exist which are effective for cancers in dogs and cats. Most of tumors in dogs and cats are realized by owners only after they advanced to grow bigger, and in many cases, it is already too late to visit a hospital to receive surgical excision of the tumor or administration of a human drug (an anticancer preparation or the like), so that those dogs and cats often die shortly after the treatment. Under such circumstances, if therapeutic agents and prophylactic agents for cancer effective for dogs and cats become available, their uses for canine cancers are expected to be developed.
Since early detection of cancer leads to good treatment results, a method for detecting cancer which can be easily carried out by testing serum, urine or the like without physical and economical burden to cancer patients is demanded. Recently, methods wherein tumor products such as tumor markers are measured have been widely used as diagnostic methods using blood or urine. Examples of the tumor products include tumor-related antigens, enzymes, specific proteins, metabolites, tumor genes, products of tumor genes, and tumor-suppressor genes, and, in some cancers, a carcinoembryonic antigen CEA, glycoproteins CA19-9 and CA125, a prostate-specific antigen PSA, calcitonin which is a peptide hormone produced in thyroid, and the like are utilized as tumor markers in cancer diagnosis (Non-patent Literature 10). However, in most types of cancers, there are no tumor markers useful for cancer diagnosis. Further, since most of the tumor markers currently known exist only in very small amounts (e.g., in the order of pg/mL) in body fluid, their detection requires a highly sensitive measurement method or a special technique. Under such circumstances, if a novel cancer detection method by which various cancers can be detected by simple operations is provided, its use for diagnosis of various cancers are expected to be developed.
CD179b is known to be a part of the surrogate light chain of immunoglobulin and to be expressed on the membrane surfaces of precursor cells of B cells (pre-B cells and pro-B cells). It disappears upon differentiation of B cells and is not expressed in mature B cells. However, CD179b is known to be expressed in leukemia (pre-B cell leukemia) cells produced by cancerization of pre-B cells (Non-patent Literatures 10 and 11). Further, CD179b is known to be expressed also in lymphoma (pre-B cell lymphoma) cells produced by cancerization of pre-B cells, and able to be used as a diagnostic marker for pre-B cell lymphoma (Non-patent Literature 12). However, its specific expression has not been reported for leukemia cells other than pre-B cell leukemia cells, lymphomas other than pre-B cell lymphoma, breast cancer cells and the like. Further, there has been no report suggesting that enhancement of immunity against CD179b is useful for therapy and/or prophylaxis of cancer.